Energy storage devices, such as Li-ion batteries, are widely used from portable electronic devices to electric cars. In the fully charged state of the battery, Li ions are typically intercalated in the anode material, such as graphite. During discharge, Li ions migrate from the anode through the electrolytes and the separator to the positive electrode where they intercalate in the positive electrode material or cause chemical conversion in it. Simultaneously, electrons migrate from the anode through the circuit outside the battery to the positive electrode, during discharge. The driving force of the process is the difference of chemical potentials of the electroactive species in the electrodes. Batteries operate until this potential difference fails to exist. During recharging this potential difference will be restored by an external power source, using currents opposite to those mentioned for discharge. While Li-ions migrate from one electrode to the other, the oxidation number of the atoms in the electrodes also changes to maintain charge neutrality of the whole of the electrodes.
Typical intercalation materials for the positive electrode involves transition metal compound nanocrystals, such as LiFePO4, LiCoO2, LiMn2O4, embedded into a carbon matrix. These materials contain channels that enable Li ion mobility for intercalation and deintercalation. The electrolyte is typically a non-aqueous liquid, such as propylene carbonate, glymes, ionic liquids or polymer electrolytes. A membrane, passable for Li ions only, separates the negative and positive electrode spaces.
The performance of Li-ion batteries depends on the choice of the electrode materials and on the other components of the battery. Batteries that intercalate other than Li-ions are also known, for example Na ion batteries (S. Ohmori and T. Yamamoto, “Sodium ion battery”, US 2012/0021273 A1), or K ion batteries (A. Eftekhari (2004), “Potassium secondary cell based on Prussian blue cathode,” Journal of Power Sources 126, 221).
There remains a need for increased charge and discharge rates, while also allowing for similarly high or even higher gravimetric and volumetric energy densities and capacities as compared to traditional Li-ion batteries. The present invention is directed to meeting this need, including by way of using functionalized boron nitride materials as electroactive materials in the electrodes of energy storage devices, such as rechargeable batteries.